This study will examine the perception of natural and synthetic communication calls by two parrot species. Categorical perception is considered to occur when continuously varying stimuli are perceptually classified into a discrete group and there is increased discriminability of variants across categorical boundaries. In this project, three separate experiments will test whether either the yellow-nape amazon or the budgerigar 1) has categorical perception of yellow-nape amazon vocalizations, and if so 2) whether both species perceive similar categories in the same set of calls. The first experiment will test the basic auditory sensitivities of the yellow-nape amazon and compare them to available audiograms for the budgerigar and other bird species. The second experiment will compare the abilities of the two species to discriminate among novel variants of natural calls of the yellow-nape amazon and test whether either species has perceptual categories that correspond to previously defined acoustic categories. The third experiment will compare the abilities of the two species to discriminate between equally spaced synthetic variants and test for the existence of the sharp boundaries in discriminability between variants characteristic of categorical perception. In sum, these experiments will begin to address two general questions: first, whether natural calls are perceived in a categorical fashion by animals and, second, whether these categories are species-specific (restricted to a species own calls) or are general (found for both conspecific and heterospecific calls). The proposed project will provide valuable training in methods for signal synthesis, acoustic analysis, and psychoacoustical testing. It will also contribute to the development of a model system with great potential for the study of auditory perception and vocal learning.